Primary cardiomyocyte-targeted bioreducible polymer for efficient gene delivery to the myocardium

Phage-based delivery systems: engineering, applications, and challenges in nanomedicines

Bacteriophages (phages) represent a unique category of viruses with a remarkable ability to selectively infect host bacteria, characterized by their assembly from proteins and nucleic acids. Leveraging their exceptional biological properties and modifiable characteristics, phages emerge as innovative, safe, and efficient delivery vectors. The potential drawbacks associated with conventional nanocarriers in the realms of drug and gene delivery include a lack of cell-specific targeting, cytotoxicity, and diminished in vivo transfection efficiency. In contrast, engineered phages, when employed as cargo delivery vectors, hold the promise to surmount these limitations and attain enhanced delivery efficacy. This review comprehensively outlines current strategies for the engineering of phages, delineates the principal types of phages utilized as nanocarriers in drug and gene delivery, and explores the application of phage-based delivery systems in disease therapy. Additionally, an incisive analysis is provided, critically examining the challenges confronted by phage-based delivery systems within the domain of nanotechnology. The primary objective of this article is to furnish a theoretical reference that contributes to the reasoned design and development of potent phage-based delivery systems.

Exosome-based WTAP siRNA delivery ameliorates myocardial ischemia-reperfusion injury

Myocardial ischemia/reperfusion (MI/R) injury is the primary cause of postischemicheartfailure. The increased expression of Thioredoxin-interacting protein (TXNIP) has been implicated in MI/R injury, although the detailed mechanism remains incompletely understood. In the present study, we observed the up-regulation of the m6A mRNA methylation complex component Wilms' tumor 1-associating protein (WTAP) in MI/R mice, which led to the m6A modification of TXNIP mRNA and an increase in mRNA abundance. Knock-down of WTAP resulted in a significant reduction in the m6A level of TXNIP mRNA and down-regulated TXNIP expression. Moreover, exosomes engineered with ischemic myocardium-targeting peptide (IMTP) were able to deliver WTAP siRNA into ischemic myocardial tissues, resulting in a specific gene knockdown and myocardial protection. In summary, our findings demonstrate that the WTAP-TXNIP regulatory axis plays a significant role in postischemicheartfailure, and the use of engineered exosomes targeting the ischemic heart shows promise as a strategy for siRNA therapy to protect the heart from injury.

CRISPR-Cas9 delivery strategies with engineered extracellular vesicles

Therapeutic genome editing has the potential to cure diseases by directly correcting genetic mutations in tissues and cells. Recent progress in the CRISPR-Cas9 systems has led to breakthroughs in gene editing tools because of its high orthogonality, versatility, and efficiency. However, its safe and effective administration to target organs in patients is a major hurdle. Extracellular vesicles (EVs) are endogenous membranous particles secreted spontaneously by all cells. They are key actors in cell-to-cell communication, allowing the exchange of select molecules such as proteins, lipids, and RNAs to induce functional changes in the recipient cells. Recently, EVs have displayed their potential for trafficking the CRISPR-Cas9 system during or after their formation. In this review, we highlight recent developments in EV loading, surface functionalization, and strategies for increasing the efficiency of delivering CRISPR-Cas9 to tissues, organs, and cells for eventual use in gene therapies.

Nanotherapeutics for the Myocardium: A Potential Alternative for Treating Cardiac Diseases

ABSTRACT

Cardiovascular diseases (CVDs) are the foremost cause of morbidity and mortality worldwide. Current clinical interventions include invasive approaches for progressed conditions and pharmacological assistance for initial stages, which has systemic side effects. Preventive, curative, diagnostic, and theranostic (therapeutic + diagnostic) approaches till date are not very useful in combating the ongoing CVD epidemic, which demands a promising efficient alternative approach. To combat the growing CVD outbreak globally, the ideal strategy is to make the therapeutic intervention least invasive and direct to the heart to reduce the bystander effects on other organs and increase the bioavailability of the therapeutics to the myocardium. The application of nanoscience and nanoparticle-mediated approaches have gained a lot of momentum because of their efficient passive and active myocardium targeting capability owing to their improved specificity and controlled release. This review provides extensive insight into the various types of nanoparticles available for CVDs, their mechanisms of targeting (eg, direct or indirect), and the utmost need for further development of bench-to-bedside cardiac tissue-based nanomedicines. Furthermore, the review aims to summarize the different ideas and methods of nanoparticle-mediated therapeutic approaches to the myocardium till date with present clinical trials and future perspectives. This review also reflects the potential of such nanoparticle-mediated tissue-targeted therapies to contribute to the sustainable development goals of good health and well-being.

Phage for drug delivery vehicles

Viruses being the natural carriers of gene have been widely used as drug delivery systems. However, the commonly used eukaryotic viruses such as adenoviruses, retroviruses, and lentiviruses, besides efficiently targeting the cells, can also stimulate immunological response or disrupt tumour suppressor genes leading to cancer. Consequently, there has been an increase interest in the scientific fraternity towards exploring other alternatives, which are safer and equally efficient for drug delivery. Bacteriophages, in this context have been at the forefront as an efficient, reliable, and safer choice. Novel phage dependent technologies led the foundation of peptide libraries and provides way to recognising abilities and targeting of specific ligands. Hybridisation of phage with inorganic complexes could be an appropriate strategy for the construction of carrying bioinorganic carriers. In this chapter, we have tried to cover major advances in the phage species that can be used as drug delivery vehicles.

Illuminating the Molecular Intricacies of Exosomes and ncRNAs in Cardiovascular Diseases: Prospective Therapeutic and Biomarker Potential

Cardiovascular diseases (CVDs) are one of the leading causes of death worldwide. Accumulating evidences have highlighted the importance of exosomes and non-coding RNAs (ncRNAs) in cardiac physiology and pathology. It is in general consensus that exosomes and ncRNAs play a crucial role in the maintenance of normal cellular function; and interestingly it is envisaged that their potential as prospective therapeutic candidates and biomarkers are increasing rapidly. Considering all these aspects, this review provides a comprehensive overview of the recent understanding of exosomes and ncRNAs in CVDs. We provide a great deal of discussion regarding their role in the cardiovascular system, together with providing a glimpse of ideas regarding strategies exploited to harness their potential as a therapeutic intervention and prospective biomarker against CVDs. Thus, it could be envisaged that a thorough understanding of the intricacies related to exosomes and ncRNA would seemingly allow their full exploration and may lead clinical settings to become a reality in near future.

Non-Viral Gene Delivery Systems for Treatment of Myocardial Infarction: Targeting Strategies and Cardiac Cell Modulation

Cardiovascular diseases (CVD) are the leading cause of morbidity and mortality worldwide. Conventional therapies involving surgery or pharmacological strategies have shown limited therapeutic effects due to a lack of cardiac tissue repair. Gene therapy has opened an avenue for the treatment of cardiac diseases through manipulating the underlying gene mechanics. Several gene therapies for cardiac diseases have been assessed in clinical trials, while the clinical translation greatly depends on the delivery technologies. Non-viral vectors are attracting much attention due to their safety and facile production compared to viral vectors. In this review, we discuss the recent progress of non-viral gene therapies for the treatment of cardiovascular diseases, with a particular focus on myocardial infarction (MI). Through a summary of delivery strategies with which to target cardiac tissue and different cardiac cells for MI treatment, this review aims to inspire new insights into the design/exploitation of non-viral delivery systems for gene cargos to promote cardiac repair/regeneration.

Peptide-Modified Biopolymers for Biomedical Applications

Polymeric biomaterials have been used in a variety of applications, like cargo delivery and tissue scaffolding, because they are easily synthesized and can be adapted to many systems. However, there is still a need to further enhance and improve their functions to progress their use in the biomedical field. A promising solution is to modify the polymer surfaces with peptides that can increase biocompatibility, cellular interactions, and receptor targeting. In recent years, peptide modifications have been used to overcome many challenges to polymer biomaterial development. This review discusses recent progress in developing peptide-modified polymers for therapeutic applications including cell-specific targeting and tissue engineering. Furthermore, we will explore some of the most frequently studied base components of these biomaterials.

Nanostructured Polymeric, Liposomal and Other Materials to Control the Drug Delivery for Cardiovascular Diseases

Cardiovascular diseases (CVDs) are the leading cause of death globally, taking an estimated 17.9 million lives each year, representing one third of global mortality. As existing therapies still have limited success, due to the inability to control the biodistribution of the currently approved drugs, the quality of life of these patients is modest. The advent of nanomedicine has brought new insights in innovative treatment strategies. For this reason, several novel nanotechnologies have been developed for both targeted and prolonged delivery of therapeutics to the cardiovascular system tο minimize side effects. In this regard, nanoparticles made of natural and/or synthetic nanomaterials, like liposomes, polymers or inorganic materials, are emerging alternatives for the encapsulation of already approved drugs to control their delivery in a targeted way. Therefore, nanomedicine has attracted the attention of the scientific community as a potential platform to deliver therapeutics to the injured heart. In this review, we discuss the current types of biomaterials that have been investigated as potential therapeutic interventions for CVDs as they open up a host of possibilities for more targeted and effective therapies, as well as minimally invasive treatments.

Phage nanofibers in nanomedicine: Biopanning for early diagnosis, targeted therapy, and proteomics analysis

Display of a peptide or protein of interest on the filamentous phage (also known as bacteriophage), a biological nanofiber, has opened a new route for disease diagnosis and therapy as well as proteomics. Earlier phage display was widely used in protein-protein or antigen-antibody studies. In recent years, its application in nanomedicine is becoming increasingly popular and encouraging. We aim to review the current status in this research direction. For better understanding, we start with a brief introduction of basic biology and structure of the filamentous phage. We present the principle of phage display and library construction method on the basis of the filamentous phage. We summarize the use of the phage displayed peptide library for selecting peptides with high affinity against cells or tissues. We then review the recent applications of the selected cell or tissue targeting peptides in developing new targeting probes and therapeutics to advance the early diagnosis and targeted therapy of different diseases in nanomedicine. We also discuss the integration of antibody phage display and modern proteomics in discovering new biomarkers or target proteins for disease diagnosis and therapy. Finally, we propose an outlook for further advancing the potential impact of phage display on future nanomedicine. This article is categorized under: Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

Exosomes Engineered to Express a Cardiomyocyte Binding Peptide Demonstrate Improved Cardiac Retention in Vivo

Injury to the heart results in cardiomyocyte cell death and can lead to pathological remodeling of remaining cells, contributing to heart failure. Despite the therapeutic potential of new drugs and small molecules, there remains a gap in the ability to efficiently deliver cardioprotective agents in a cell specific manner while minimizing nonspecific delivery to other organs. Exosomes derived from cardiosphere-derived cells (CDCs) have been shown to stimulate angiogenesis, induce endogenous cardiomyocyte proliferation and modulate cardiomyocyte apoptosis and hypertrophy. While innately cardioprotective at high doses, unmodified CDC-exosomes demonstrate limited cardiac tropism. To generate an efficient exosomal delivery system that can target cardiomyocytes, we engineered CDCs to express Lamp2b, an exosomal membrane protein, fused to a cardiomyocyte specific peptide (CMP), WLSEAGPVVTVRALRGTGSW. Exosomes isolated from engineered CDCs expressed CMP on their surface and retained their native physical properties. Targeted exosomes resulted in increased uptake by cardiomyocytes, decreased cardiomyocyte apoptosis, and higher cardiac retention following intramyocardial injection when compared with non-targeted exosomes. Importantly, we established a novel targeting system to improve exosomal uptake by cardiomyocytes and laid the foundation for cell-specific exosomal delivery of drug and gene therapies to improve the functional capacity of the heart following both ischemic and non-ischemic injury.

Functionalization of soft materials for cardiac repair and regeneration

Coronary artery disease is a leading cause of death in developed nations. As the disease progresses, myocardial infarction can occur leaving areas of dead tissue in the heart. To compensate, the body initiates its own repair/regenerative response in an attempt to restore function to the heart. These efforts serve as inspiration to researchers who attempt to capitalize on the natural regenerative processes to further augment repair. Thus far, researchers are exploiting these repair mechanisms in the functionalization of soft materials using a variety of growth factor-, ligand- and peptide-incorporating approaches. The goal of functionalizing soft materials is to best promote and direct the regenerative responses that are needed to restore the heart. This review summarizes the opportunities for the use of functionalized soft materials for cardiac repair and regeneration, and some of the different strategies being developed.

Nanoparticle-mediated siRNA Gene-silencing in Adult Zebrafish Heart

Mammals have a very limited capacity to regenerate the heart after myocardial infarction. On the other hand, the adult zebrafish regenerates its heart after apex resection or cryoinjury, making it an important model organism for heart regeneration study. However, the lack of loss-of-function methods for adult organs has restricted insights into the mechanisms underlying heart regeneration. RNA interference via different delivery systems is a powerful tool for silencing genes in mammalian cells and model organisms. We have previously reported that siRNA-encapsulated nanoparticles successfully enter cells and result in a remarkable gene-specific knockdown in the regenerating adult zebrafish heart. Here, we present a simple, rapid, and efficient protocol for the dendrimer-mediated siRNA delivery and gene-silencing in the regenerating adult zebrafish heart. This method provides an alternative approach for determining gene functions in adult organs in zebrafish and can be extended to other model organisms as well.

Cardiomyocyte-targeted and 17β-estradiol-loaded acoustic nanoprobes as a theranostic platform for cardiac hypertrophy

Background

Theranostic perfluorocarbon nanoprobes have recently attracted attention due to their fascinating versatility in integrating diagnostics and therapeutics into a single system. Furthermore, although 17β-estradiol (E2) is a potential anti-hypertrophic drug, it has severe non-specific adverse effects in various organs. Therefore, we have developed cardiomyocyte-targeted theranostic nanoprobes to achieve concurrent targeted imaging and treatment of cardiac hypertrophy.

Results

We had successfully synthesized E2-loaded, primary cardiomyocyte (PCM) specific peptide-conjugated nanoprobes with perfluorocarbon (PFP) as a core (PCM-E2/PFPs) and demonstrated their stability and homogeneity. In vitro and in vivo studies confirmed that when exposed to low-intensity focused ultrasound (LIFU), these versatile PCM-E2/PFPs can be used as an amplifiable imaging contrast agent. Furthermore, the significantly accelerated release of E2 enhanced the therapeutic efficacy of the drug and prevented systemic side effects. PCM-E2/PFPs + LIFU treatment also significantly increased cardiac targeting and circulation time. Further therapeutic evaluations showed that PCM-E2/PFPs + LIFU suppressed cardiac hypertrophy to a greater extent compared to other treatments, revealing high efficiency in cardiac-targeted delivery and effective cardioprotection.

Conclusion

Our novel theranostic nanoplatform could serve as a potential theranostic vector for cardiac diseases.

Electronic supplementary material

The online version of this article (10.1186/s12951-018-0360-3) contains supplementary material, which is available to authorized users.

PCM and TAT co-modified liposome with improved myocardium delivery: in vitro and in vivo evaluations

In this study, PCM and TAT co-modified liposome was developed as a novel drug carrier for myocardium delivery with evaluation of its in vitro and in vivo properties. Liposomes containing fluorescent probe coumarin-6 were prepared by thin-film hydration. The PCM ligands specifically bind to the PCM receptors in the extracellular connective tissue of primary myocardium cells (MCs), while the TAT ligands functioned as a classical cell penetrating peptide to make liposomes internalized by MCs. The unmodified liposome (L), PCM-modified liposome (PL), TAT-modified liposome (TL) and PCM and TAT co-modified liposome (PTL) were prepared and characterized. The cellular uptake and intracellular distribution of various liposomes by MCs demonstrated that PTL had the best delivery capability. Peptide inhibition assay indicated that the uptake of PL could be inhibited by PCM. However, TAT could almost not suppress the uptake of TL. In addition, the CCK-8 experiments showed that liposomes had low cytotoxicity. In vivo fluorescent images of frozen sections and HPLC-fluorescence analysis further demonstrated that PTL had highest myocardium distribution. The results of this study demonstrated that PCM and TAT co-modifying could improve the myocardial targeting ability of liposome.

Exploring the role of peptides in polymer-based gene delivery

Polymers are widely studied as non-viral gene vectors because of their strong DNA binding ability, capacity to carry large payload, flexibility of chemical modifications, low immunogenicity, and facile processes for manufacturing. However, high cytotoxicity and low transfection efficiency substantially restrict their application in clinical trials. Incorporating functional peptides is a promising approach to address these issues. Peptides demonstrate various functions in polymer-based gene delivery systems, such as targeting to specific cells, breaching membrane barriers, facilitating DNA condensation and release, and lowering cytotoxicity. In this review, we systematically summarize the role of peptides in polymer-based gene delivery, and elaborate how to rationally design polymer-peptide based gene delivery vectors.

STATEMENT OF SIGNIFICANCE

Polymers are widely studied as non-viral gene vectors, but suffer from high cytotoxicity and low transfection efficiency. Incorporating short, bioactive peptides into polymer-based gene delivery systems can address this issue. Peptides demonstrate various functions in polymer-based gene delivery systems, such as targeting to specific cells, breaching membrane barriers, facilitating DNA condensation and release, and lowering cytotoxicity. In this review, we highlight the peptides' roles in polymer-based gene delivery, and elaborate how to utilize various functional peptides to enhance the transfection efficiency of polymers. The optimized peptide-polymer vectors should be able to alter their structures and functions according to biological microenvironments and utilize inherent intracellular pathways of cells, and consequently overcome the barriers during gene delivery to enhance transfection efficiency.

Peptides, polypeptides and peptide–polymer hybrids as nucleic acid carriers

Peptide, polypeptide and polymer–peptide hybrid based nucleic acid therapeutics (NAT).

Cationic cell-penetrating peptides as vehicles for siRNA delivery

RNA interference mediated gene silencing has tremendous applicability in fields ranging from basic biological research to clinical therapy. However, delivery of siRNA across the cell membrane into the cytoplasm, where the RNA silencing machinery is located, is a significant hurdle in most primary cells. Cell-penetrating peptides (CPPs), peptides that possess an intrinsic ability to translocate across cell membranes, have been explored as a means to achieve cellular delivery of siRNA. Approaches using CPPs by themselves or through incorporation into other siRNA delivery platforms have been investigated with the intent of improving cytoplasmic delivery. Here, we review the utilization of CPPs for siRNA delivery with a focus on strategies developed to enhance cellular uptake, endosomal escape and cytoplasmic localization of CPP/siRNA complexes.

Self-Healing Conductive Injectable Hydrogels with Antibacterial Activity as Cell Delivery Carrier for Cardiac Cell Therapy

Cell therapy is a promising strategy to regenerate cardiac tissue for myocardial infarction. Injectable hydrogels with conductivity and self-healing ability are highly desirable as cell delivery vehicles for cardiac regeneration. Here, we developed self-healable conductive injectable hydrogels based on chitosan-graft-aniline tetramer (CS-AT) and dibenzaldehyde-terminated poly(ethylene glycol) (PEG-DA) as cell delivery vehicles for myocardial infarction. Self-healed electroactive hydrogels were obtained after mixing CS-AT and PEG-DA solutions at physiological conditions. Rapid self-healing behavior was investigated by rheometer. Swelling behavior, morphology, mechanical strength, electrochemistry, conductivity, adhesiveness to host tissue and antibacterial property of the injectable hydrogels were fully studied. Conductivity of the hydrogels is ∼10(-3) S·cm(-1), which is quite close to native cardiac tissue. Proliferation of C2C12 myoblasts in the hydrogel showed its good biocompatibility. After injection, viability of C2C12 cells in the hydrogels showed no significant difference with that before injection. Two different cell types were successfully encapsulated in the hydrogels by self-healing effect. Cell delivery profile of C2C12 myoblasts and H9c2 cardiac cells showed a tunable release rate, and in vivo cell retention in the conductive hydrogels was also studied. Subcutaneous injection and in vivo degradation of the hydrogels demonstrated their injectability and biodegradability. Together, these self-healing conductive biodegradable injectable hydrogels are excellent candidates as cell delivery vehicle for cardiac repair.

Poly(Amido Amine)s Containing Agmatine and Butanol Side Chains as Efficient Gene Carriers

A new type of bioreducible poly(amido amine) copolymer is synthesized by the Michael addition polymerization of cystamine bisacrylamide (CBA) with 4-aminobutylguanidine (agmatine, AGM) and 4-aminobutanol (ABOL). Since the positively charged guanidinium groups of AGM and the hydroxybutyl groups of ABOL in the side chains have shown to improve the overall transfection efficiency of poly(amido amine)s, it is hypothesized that poly(CBA-ABOL/AGM) synthesized at the optimal ratio of both components would result in high transfection efficiency and minimal toxicity. In this study, a series of the poly(CBA-ABOL/AGM) copolymers is synthesized as gene carriers. The polymers are characterized and luciferase transfection efficiencies of the polymers in various cell lines are investigated to select the ideal ratio between AGM and ABOL. The poly(CBA-ABOL/AGM) containing 80% AGM and 20% ABOL has shown the best transfection efficiency with the lowest cytotoxicity, indicating that this polymer is very promising as a potent and nontoxic gene carrier.

Nanovector-based prolyl hydroxylase domain 2 silencing system enhances the efficiency of stem cell transplantation for infarcted myocardium repair

Mesenchymal stem cell (MSC) transplantation has attracted much attention in myocardial infarction therapy. One of the limitations is the poor survival of grafted cells in the ischemic microenvironment. Small interfering RNA-mediated prolyl hydroxylase domain protein 2 (PHD2) silencing in MSCs holds tremendous potential to enhance their survival and paracrine effect after transplantation. However, an efficient and biocompatible PHD2 silencing system for clinical application is lacking. Herein, we developed a novel PHD2 silencing system based on arginine-terminated generation 4 poly(amidoamine) (Arg-G4) nanoparticles. The system exhibited effective and biocompatible small interfering RNA delivery and PHD2 silencing in MSCs in vitro. After genetically modified MSC transplantation in myocardial infarction models, MSC survival and paracrine function of IGF-1 were enhanced significantly in vivo. As a result, we observed decreased cardiomyocyte apoptosis, scar size, and interstitial fibrosis, and increased angiogenesis in the diseased myocardium, which ultimately attenuated ventricular remodeling and improved heart function. This work demonstrated that an Arg-G4 nanovector-based PHD2 silencing system could enhance the efficiency of MSC transplantation for infarcted myocardium repair.

Functional polymers of gene delivery for treatment of myocardial infarct

Ischemic heart disease is rapidly growing as the common cause of death in the world. It is a disease that occurs as a result of coronary artery stenosis and is caused by the lack of oxygen within cardiac muscles due to an imbalance between oxygen supply and demand. The conventional medical therapy is focused on the use of drug eluting stents, coronary-artery bypass graft surgery and anti-thrombosis. Gene therapy provides great opportunities for treatment of cardiovascular disease. In order for gene therapy to be successful, the development of proper gene delivery systems and hypoxia-regulated gene expression vectors is the most important factors. Several non-viral gene transfer methods have been developed to overcome the safety problems of viral transduction. Some of which include plasmids that regulate gene expression that is controlled by environment specific promoters in the transcriptional or the translational level. This review explores polymeric gene carriers that target the myocardium and hypoxia-inducible vectors, which regulate gene expression in response to hypoxia, and their application in animal myocardial infarction models.

Bioreducible polymers for therapeutic gene delivery

Most currently available cationic polymers have significant acute toxicity concerns such as cellular toxicity, aggregation of erythrocytes, and entrapment in the lung capillary bed, largely due to their poor biocompatibility and non-degradability under physiological conditions. To develop more intelligent polymers, disulfide bonds are introduced in the design of biodegradable polymers. Herein, the sustained innovations of biomimetic nano-sized constructs with bioreducible poly(disulfide amine)s demonstrate a viable clinical tool for the treatment of cardiovascular disease, anemia, diabetes, and cancer.

Plasmid DNA hydrogels for biomedical applications

In the last few years, our research group has focused on the design and development of plasmid DNA (pDNA) based systems as devices to be used therapeutically in the biomedical field. Biocompatible macro and micro plasmid DNA gels were prepared by a cross-linking reaction. For the first time, the pDNA gels have been investigated with respect to their swelling in aqueous solution containing different additives. Furthermore, we clarified the fundamental and basic aspects of the solute release mechanism from pDNA hydrogels and the significance of this information is enormous as a basic tool for the formulation of pDNA carriers for drug/gene delivery applications. The co-delivery of a specific gene and anticancer drugs, combining chemical and gene therapies in the treatment of cancer was the main challenge of our research. Significant progresses have been made with a new p53 encoding pDNA microgel that is suitable for the loading and release of pDNA and doxorubicin. This represents a strong valuable finding in the strategic development of systems to improve cancer cure through the synergetic effect of chemical and gene therapy.

"Bio"-macromolecules: polymer-protein conjugates as emerging scaffolds for therapeutics

Polymer-protein conjugates are biohybrid macromolecules derived from covalently connecting synthetic polymers with polypeptides. The resulting materials combine the properties of both worlds: chemists can engineer polymers to stabilize proteins, to add functionality, or to enhance activity; whereas biochemists can exploit the specificity and complexity that Nature has bestowed upon its macromolecules. This has led to a wealth of applications, particularly within the realm of biomedicine. Polymer-protein conjugation has expanded to include scaffolds for drug delivery, tissue engineering, and microbial inhibitors. This feature article reflects upon recent developments in the field and discusses the applications of these hybrids from a biomaterials standpoint.

Functionalized dendrimer-based delivery of angiotensin type 1 receptor siRNA for preserving cardiac function following infarction

Cardiovascular disease (CVD) is the leading cause of death throughout the world and much pathology is associated with upregulation of inflammatory genes. Gene silencing using RNA interference is a powerful tool in regulating gene expression, but its application in CVDs has been prevented by the lack of efficient delivery systems. We report here the development of tadpole dendrimeric materials for siRNA delivery in a rat ischemia-reperfusion (IR) model. Angiotensin II (Ang II) type 1 receptor (AT1R), the major receptor that mediates most adverse effects of Ang II, was chosen to be the silencing targeting. Among the three tadpole dendrimers synthesized, the oligo-arginine conjugated dendrimer loaded with siRNA demonstrated effective down-regulation in AT1R expression in cardiomyocytes in vitro. When the dendrimeric material was applied in vivo, the siRNA delivery prevented the increase in AT1R levels and significantly improved cardiac function recovery compared to saline injection or empty dendrimer treated groups after IR injury. These experiments demonstrate a potential treatment for dysfunction caused by IR injury and may represent an alternative to AT1R blockade.

Targeted gene delivery to ischemic myocardium by homing peptide-guided polymeric carrier

Myocardial ischemia needs an alternative treatment such as gene therapy for the direct protection of cardiomyocytes against necrosis or apoptosis and to prevent the development of myocardial fibrosis and cardiac dysfunction. Despite the utility of gene therapy, its therapeutic use is limited due to inadequate transfection in cardiomyocytes and difficulty in directing to ischemic myocardium. Here, we present a polymeric gene carrier that is capable of targeting ischemic myocardium, resulting in high localization within the ischemic zone of the left ventricle (LV) of an ischemia/reperfusion (I/R) rat model upon systemic administration. Cystamine bisacrylamide-diamino hexane (CD) polymer was modified with the ischemic myocardium-targeted peptide (IMTP) and D-9-arginine (9R) for dual effects of the homing to ischemic myocardium and enhanced transfection efficiency with minimized polymer use. Conjugation of IMTP and 9R to CD led to an increase in transfection under hypoxia and significantly reduced the amount of polymer required for high transfection. Finally, we confirmed targeting of IMTP-CD-9R/DNA polyplex to ischemic myocardium and enhanced gene expression in LV of the I/R rat after tail vein injection. This study provides a clue that gene therapy for the treatment of myocardial ischemia can be achieved by using homing peptide-guided gene delivery systems.

Cell targeting peptide conjugation to siRNA polyplexes for effective gene silencing in cardiomyocytes

To deliver siRNA specifically to cardiomyocytes with a high transfection efficiency, primary cardiomyocyte-targeting (PCM) and/or cell-penetrating (Tat) peptides were incorporated into the siRNA. With the addition of plasmid DNA, these peptide-conjugated siRNAs were able to form compact and stable nanosized polyplex particles with bioreducible poly(CBA-DAH). The peptide-modified siRNA polyplexes enhanced the cellular uptake and the gene-silencing capacity of the siRNA in cardiomyocytes without significant immunogenicity or cytotoxicity. These findings demonstrate that the cell-targeting peptide and/or cell-penetrating peptide conjugation of siRNA may be a potentially important strategy for cell-specific gene therapy in gene-mediated disease states.

Post-translational regulated and hypoxia-responsible VEGF plasmid for efficient secretion

Gene therapy using angiogenic genes has emerged as a potentially viable alternative treatment strategy for myocardial ischemia. Non-specific expression of angiogenic genes, however, may result in side effects, including the growth of occult tumors. Regulation of gene expression may help to avoid the occurrence of these side effects. In this study, a plasmid expressing vascular endothelial growth factor (VEGF) was constructed with an oxygen dependent degradation (ODD) domain and a secretion signal peptide (SP) in order to stabilize the VEGF protein and facilitate the secretion of VEGF protein, specifically under hypoxic conditions. We found that this plasmid, pβ-SP-ODD-VEGF, expresses the SP-ODD-VEGF protein at increased levels under hypoxic conditions compared to normoxic conditions. Since the size of the ODD domain is almost the same as that of VEGF, the ODD-VEGF fusion protein may have lower secretion efficiency. To address this issue, a furin recognition site was located between the ODD domain and the VEGF site to facilitate elimination of the SP-ODD domain from the fusion protein before its secretion. This optimizes the likelihood that the VEGF secreted from the target cells will be wild-type VEGF. Treatment with a furin inhibitor reduced the secretion efficiency of the VEGF, indicating that furin digestion increases the secretion of VEGF. The secreted wild-type VEGF facilitated the growth of endothelial cells more efficiently under hypoxic conditions than normoxic conditions. These results suggest that this plasmid, pβ-SP-ODD-VEGF, warrants further study as a more efficient form of hypoxia-inducible gene therapy for the treatment of myocardial ischemia.

Delivery of intracellular-acting biologics in pro-apoptotic therapies

The recent elucidation of molecular regulators of apoptosis and their roles in cellular oncogenesis has motivated the development of biomacromolecular anticancer therapeutics that can activate intracellular apoptotic signaling pathways. Pharmaceutical scientists have employed a variety of classes of biologics toward this goal, including antisense oligodeoxynucleotides, small interfering RNA, proteins, antibodies, and peptides. However, stability in the in vivo environment, tumor-specific biodistribution, cell internalization, and localization to the intracellular microenvironment where the targeted molecule is localized pose significant challenges that limit the ability to directly apply intracellular-acting, pro-apoptotic biologics for therapeutic use. Thus, approaches to improve the pharmaceutical properties of therapeutic biomacromolecules are of great significance and have included chemically modifying the bioactive molecule itself or formulation with auxiliary compounds. Recently, promising advances in delivery of pro-apoptotic biomacromolecular agents have been made using tools such as peptide "stapling", cell penetrating peptides, fusogenic peptides, liposomes, nanoparticles, smart polymers, and synergistic combinations of these components. This review will discuss the molecular mediators of cellular apoptosis, the respective mechanisms by which these mediators are dysregulated in cellular oncogenesis, the history and development of both nucleic-acid and amino-acid based drugs, and techniques to achieve intracellular delivery of these biologics. Finally, recent applications where pro-apoptotic functionality has been achieved through delivery of intracellular-acting biomacromolecular drugs will be highlighted.

Targeted delivery of non-viral vectors to cartilage in vivo using a chondrocyte-homing peptide identified by phage display

Gene therapy is a promising method for osteoarthritis and cartilage injury. However, specifically delivering target genes into chondrocytes is a great challenge because of their non-vascularity and the dense extracellular matrix of cartilage. In our study, we identified a chondrocyte-affinity peptide (CAP, DWRVIIPPRPSA) by phage display technology. Subsequent analysis suggests that the peptide can efficiently interact specifically with chondrocytes without any species specificity. Polyethylenimine (PEI) was covalently modified with CAP to construct a non-viral vector for cartilage-targeted therapy. To investigate the cartilage-targeting property of the CAP-modified vector, FITC-labeled CAP conjugated PEI/DNA particles were injected into rabbit knee joints, and visualized under confocal microscope. Higher concentrations of CAP-modified vector were detected in the cartilage and specifically taken up by chondrocytes compared with a randomly scrambled peptide (SP)-modified vector. To evaluate cartilage-targeting transfection efficiency, the GFP and luciferase genes were delivered into knee joints using CAP- and SP-modified PEI. Cartilage transfections mediated by CAP-modified PEI were much more efficient and specific than those by SP-modified PEI. This result suggests that CAP-modified PEI could be used as a specific cartilage-targeting vector for cartilage disorders.

Substrates for cardiovascular tissue engineering

Cardiovascular tissue engineering aims to find solutions for the suboptimal regeneration of heart valves, arteries and myocardium by creating 'living' tissue replacements outside (in vitro) or inside (in situ) the human body. A combination of cells, biomaterials and environmental cues of tissue development is employed to obtain tissues with targeted structure and functional properties that can survive and develop within the harsh hemodynamic environment of the cardiovascular system. This paper reviews the up-to-date status of cardiovascular tissue engineering with special emphasis on the development and use of biomaterial substrates. Key requirements and properties of these substrates, as well as methods and readout parameters to test their efficacy in the human body, are described in detail and discussed in the light of current trends toward designing biologically inspired microenviroments for in situ tissue engineering purposes.

RNA interference therapy via functionalized scaffolds

Tissue engineering aims to provide structural and biomolecular cues to compromised tissues through scaffolds. An emerging biomolecular cue is that of RNA interference by which the expression of genes can be silenced through a potent endogenous pathway. Recombinant viral-based approaches in RNAi delivery exist; however non-viral strategies offer many opportunities to exploit this mechanism of regulation in a safer way. Current RNAi therapies in clinical trials are without a vector (naked) or have slightly modified structures. Modification of these molecules with efficient backbone moieties for improved stability and potency, protecting and buffering them with delivery vehicles, and using scaffolds as reservoirs of delivery is at the frontier of current research. However, to enable an efficient sustained therapeutic effect scaffolds have a potentially significant role to play. This review presents non-viral delivery of RNAi that have been attempted via tissue engineered scaffolds. For RNAi to have a clinical impact, it is imperative to evaluate optimal delivery systems to ensure that the efficacy of this promising technology can be maximized.

Active targeting of RGD-conjugated bioreducible polymer for delivery of oncolytic adenovirus expressing shRNA against IL-8 mRNA

Even though oncolytic adenovirus (Ad) has been highlighted in the field of cancer gene therapy, transductional targeting and immune privilege still remain difficult challenges. The recent reports have noted the increasing tendency of adenoviral surface shielding with polymer to overcome the limits of its practical application. We previously reported the potential of the biodegradable polymer, poly(CBA-DAH) (CD) as a promising candidate for efficient gene delivery. To endow the selective-targeting moiety of tumor vasculature to CD, cRGDfC well-known as a ligand for cell-surface integrins on tumor endothelium was conjugated to CD using hetero-bifunctional cross-linker SM (PEG)(n). The cytopathic effects of oncolytic Ad coated with the polymers were much more enhanced dose-dependently when compared with that of naked Ad in cancer cells selectively. Above all, the most potent oncolytic effect was assessed with the treatment of Ad/CD-PEG(500)-RGD in all cancer cells. The enhanced cytopathic effect of Ad/RGD-conjugated polymer was specifically inhibited by blocking antibodies to integrins, but not by blocking antibody to CAR. HT1080 cells treated with Ad/CD-PEG(500)-RGD showed strong induction of apoptosis and suppression of IL-8 and VEGF expression as well. These results suggest that RGD-conjugated bioreducible polymer might be used to deliver oncolytic Ad safely and efficiently for tumor therapy.

Cell penetrating peptide conjugated bioreducible polymer for siRNA delivery

The primary cardiomyocyte-specific peptide (PCM) and the cell-penetrating peptide (CPP), HIV-Tat (49-57), were incorporated into the polymer, cystamine bisacrylamide-diaminohexane (CBA-DAH), to increase the delivery of RNAi to target cells, specifically cardiomyocytes. Interestingly, the impact of PCM and Tat conjugation on cellular uptake and transfection efficiency was greater in H9C2 rat cardiomyocytes than in NIH 3T3 cells. We examined the potential for siRNA targeting SHP-1 or Fas to inhibit the apoptosis of cardiomyocytes under hypoxic conditions using PCM and Tat-modified poly(CBA-DAH), (PCM-CD-Tat). To evaluate for efficacy in inhibiting apoptosis, either Fas siRNA/polymer or SHP-1 siRNA/polymer were transfected into cardiomyocytes treated under hypoxic and serum-deprived conditions. After incubation under hypoxic conditions, treatment with either the SHP-1 siRNA complex or the Fas siRNA complex resulted in an increase in cell viability and a reduction in LDH-cytotoxicity. The cells transfected with either of the siRNA polyplexes had a lower incidence of apoptosis as demonstrated by Annexin V-FITC/PI staining. Both the SHP-1 siRNA/PCM-CD-Tat complex and the Fas siRNA/PCM-CD-Tat complex warrant further investigation as therapeutic agents to inhibit the apoptosis of cardiomyocytes.